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Monazite, Thorium and 










Technical Paper 110 Mineral Technology 8 








The Bureau of Mines, in carrying out one of the provisions of its organic act to dis- 
seminate information concerning investigations made prints a limited free edition 
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When this edition is exhausted copies may be obtained at cost price only through 
the superintendent of documents, Government Printing Office, Washington, D. C. 

The superintendent of documents is not an official of the Bureau of Mines. His is 
an entirely separate office and he should be addressed: 


Government Printing Office, 

Washington, D. C. 

The general law under which publications are distributed prohibits the giving of 
more than one copy of a publication to one person. The cost of this publication is 5 

First edition. June, 1915. 





Introduction 5 

Properties of monazite 5 

Occurrence of monazite '. 6 

Where monazite is mined 6 

History of production of monazite 7 

First German thorium convention 7 

Second German thorium convention 8 

Causes of reduced price of thorium 9 

Consumption of monazite 9 

Prospecting for monazite deposits 10 

Use of spectroscope 10 

Monazite deposits in North and South Carolina 10 

North Carolina 11 

South Carolina 12 

Deposits in Idaho and Colorado '. . . . 12 

Idaho 12 

Colorado 13 

Deposits in Brazil 13 

Mining of monazite in the Carolinas , 14 

Milling methods in the Carolinas 16 

Electromagnetic equipment used J 6 

By-product separation .' 17 

Cost of mining and milling 17 

Comments on electromagnetic process 18 

Estimated monazite resources 19 

Duty on monazite exported from United States and Brazil 20 

United States 20 

Brazil 20 

Import duties on monazite 20 

Examination and valuation of monazite deposits 20 

Attempts to use by-products 22 

Method for the determination of thorium in monazite 23 

Treatment of monazite for the extraction of thorium 24 

Separation of mesothorium on a commercial scale 25 

Quantitative determination of mesothorium 2(5 

Minerals in monazite sands 27 

Flow sheet 2? 

Selected bibliography 30 

Publications on mineral technology 31 


FIGURE 1. Flow sheet, shdwlng steps in process of magnetic separation of 

monazite sands 





The monazite industry in the United States has been practically at 
a standstill since 1906, principally for the reason that monazite could 
he mined and obtained cheaper from Brazil, where large deposits are 
found and exploited along the seacoast and in the interior. For- 
merly part of the monazite mined in the States of North and South 
Carolina was used for the manufacture of thorium nitrate in this 
country and part of the production was sent to Germany. It seems 
an opportune time to call attention to the monazite deposits in the 
United States, as the imports of thorium nitrate are at present cur- 
tailed. There is reason to believe that a more general manufacture of 
thorium nitrate may be developed in this country. It may be many 
years before supplies of the nitrate from Europe can be depended 

There are deposits of monazite in several of our States, and with 
the knowledge that a valuable product mesothorium can be made 
as a by-product from the residues of thorium nitrate manufacture the 
industry may be developed in this country and should pay well. 
Mesothorium is used successfully in therapy in the same manner as 

With these facts in view the following description of the occurrences 
of monazite in the United States, the uses to which its products can 
be put, and the methods of mining and treatment has been prepared 
by the Bureau of Mines with the purpose of aiding more efficient 
utilization of radioactive minerals. 


Monazite is an anhydrous phosphate of the rare earths, especially 
cerium, lanthanum, neodymium, praseodymium, yttrium, and 
erbium, and contains also a small percentage of thorium. So far its 
content of thoria only gives the mineral its commercial importance, 
although a market is being developed for some of the other rare 
earths in special types of electrodes for arc lamps and in the flaming 
arc. The content of thoria in monazite is small and varies from a 
fraction of 1 per cent to about 12 per cent, although monazite con- 
taining less than 3 per cent of ThO 2 can not be used successfully in 




the manufacture of thorium nitrate, which is the important chemical 
product necessary for the manufacture of incandescent gas mantles. 
In this manufacture the thorium is mixed with 1 to 2 per cent of other 
nitrates of the rare earths. References to the percentage of thoria in 
"monazite" generally apply to a sand containing about 92 to 95 per 
cent of true monazite; such sand is sold in the market on the basis of 
its content of thoria at a fixed price per unit. 

Monazite possesses radioactive properties strong enough to affect 
a photographic plate and to be measured in the electroscope. The 
activity of the sand is due to its content of mesothorium and radium. 

The specific gravity of monazite varies from 4.9 to 5.3. It has a 
hardness of 5, is somewhat brittle, and can be easily pulverized. 

Nearly all of the monazite brought to the market is of a yellowish, 
resinous color. The Brazilian monazite of the coast lands appears to 
have a more uniform shade of color and size of grain than the mona- 
zite from the interior. The region from which monazite from the 
Carolinas has been mined can often be determined by its color alone. 
Carolinian monazite ranges from yellowish to brownish, greenish and 

grayish in color. 


Monazite is usually found in the gravel of small streams or bottom 
lands, but sometimes it is also found in the soil of hillsides. In Brazil 
it occurs also in the beach sands of the coast. In places it is found in 
small crystals in gneiss, granite, and pegmatite (crystalline) rocks. 

As these rocks become disintegrated, the crystals are washed into 
the creeks and streams _and, together with other heavy sands, are 
deposited in the beds of such watercourses. They are thus concen- 
trated in the gravel by the natural flow of the water; the lighter 
clay and quartz sand being carried away. On the coast of Brazil the 
monazite from the crystalline rocks of the coastal mountains is con- 
centrated in strata by the waves of the sea. The mountain sides are 
washed down by the strong waves at high tide and during storms. 

In some places, especially Norway, monazite is imbedded in thin 
layers of mica (biotite) in strata or, in places, in mica schists. Such 
monazite is usually of high grade but, on account of the enormous 
masses of rock material that have to be handled and crushed before 
concentration, these deposits can not be considered of commercial 
importance. The proportion of monazite in these rocks averages 
perhaps 0.01 per cent. 


Monazite has thus far been mined successfully only in North and 
South America 'in North America, in the Carolinas and in Idaho, 
and in South America in Brazil. The Brazil deposits occur along 
the coast of the States of Bahia and Espirito Santo, and also less 


abundantly on the Parahyba River in the States of Eio de Janeiro 
and Minas Geraes. Other coastal lands in the State of Rio de 
Janeiro have also been worked. Deposits of monazite sand have 
been found, too, in Swaziland, Africa, as well as in Ceylon and in 
Australia. In Jekaterinburg, Russia, it occurs in native rock and 
placers. It has also been exported from Trovancore, India. 

In the United States, occurrences of monazite are known in many 
other States than the Carolinas, but it is probable that the deposits 
in Idaho and the Carolinas alone are of importance commercially. 

Brazil has furnished the bulk of monazite for commercial use. 
Little has been mined elsewhere since the enormous price cut in the 
earlier part of 1906, as the workings in the Carolinas have been 
gradually abandoned. For some years past Brazil has furnished all 
of the monazite for the gas-mantle industry for both Europe and the 
United States. 


Although generally known to interested persons, a short history 
of the development of production and final overproduction of this 
once rare mineral may be warranted. 

The first monazite used in Europe for chemical purposes was 
brought at great expense from Sweden and Norway. 

About 27 years ago John Gordon, an American, found monazite 
on the coast of Brazil, in the State of Bahia, and brought the mineral 
in large quantities to Hamburg. The supply was sufficient to furnish 
the thorium industry of the entire world with monazite at a com- 
paratively low price. Mr. Gordon obtained a monopoly of the Bahian 
monazite sands. 

At that time the manufacture of thorium nitrate in Europe as a 
specialty was confined to a few large chemical firms in Germany and 
to the Welsbach Co. in Vienna. These were the only firms that 
provided the European market with thorium nitrate. They also 
sent large quantities of the nitrate to the United States. The 
American Welsbach Co. early manufactured thorium nitrate from 
sands mined in the Carolinas, a protective duty of 6 cents per pound 
making this possible, as the mining of monazite in this country is 
more expensive than in Brazil. 


Late in 1902 Mr. Gordon entered into an agreement with the four 
largest German manufacturers and with the Austrian manufacturer 
by which he agreed to furnish monazite at a price of $150 per metric 
ton and a percentage of the profits from the manufactured nitrates. 
With this agreement a close combination was formed which prevented 
other thorium manufacturers from acquiring any of the mineral 


mined by Mr. Gordon. The combination was known as the German 
Thorium Convention, which, after the conclusion of the agreement 
with Mr. Gordon, immediately raised the price of thorium nitrate 
100 per cent. 

Mr. Gordon's supply came from the coast lands of Bahia, near 
Prado, Brazil, and he exported the sands for a long period without 
interference. Finally the Brazilian Government became acquainted 
with the value of the resources and found an old law according to 
which all of the Brazilian coast lands along the sea and navigable 
rivers belong exclusively to the Federal Government for defensive 
purposes. The Government concluded, therefore, that no private 
individual or State government had the right to mine, sell, lease, or 
remove any of this property without the consent of Federal authority. 
In 1903 the Government of Brazil advertised that coast lands in the 
State of Espirito Santo would be leased to the highest bidder for the 
exploitation of the sands lying within its territory. 

A business man living in Rio de Janeiro made a contract with the 
Government, but for some reason allowed it to lapse. Finally an 
engineer obtained the contract for the firm of A. C. de Freitas & Co., 
of Hamburg, Germany. By the contract the firm mentioned agreed 
to pay to the Brazilian Government a rental of 50 per cent of the 
selling price of monazite sand and to export at least 1 ,200 tons annu- 
ally during the life of the contract. 


To avoid interference, the German Thorium Convention arranged, 
later on, that half of its supply should be furnished by Mr. Gordon 
and half by the De Freitas Company; and a new convention was 
formed by the four German chemical manufacturers with Mr. Gordon 
and the De Freitas Company by which the latter two were to supply 
the monazite to the four German manufacturers only and were to 
receive therefor $150 per ton of monazite and a percentage of the 
profits from the sale of the nitrates. 

As a result of the convention other firms in various countries, which 
had in the meantime begun to manufacture thorium nitrate, were 
without a supply of raw material and had to depend upon the ashes 
of spent mantles. Consequently, they made every effort to find and 
develop new deposits of monazite in Brazil, the Carolinas, and else- 
where. The whole world was searched for rare-earth minerals by 
their engineers, with the interest and assistance of many governments. 
The high price for thorium nitrate made it possible to mine monazite 
hi the Carolinas and export it to Germany; thus one German manu- 
facturer an outsider received his supply from North and South 
Carolina. Later, American firms independent of the Welsbach com- 


panies began to buy monazite in the Carolinas, and by the compe- 
tition created for a brief period caused the price for lands and monazite 
sand to rise to a point highly profitable to the farmers and landowners 
of the Carolinas. 


On account of overproduction in thorium, the price for thorium 
nitrate was suddenly dropped 50 per cent by the convention in the 
year 1906. The mining of monazite consequently decreased in all 
localities where the cost of the mining was high, as, for instance, in. 
the Carolinas. 

Since 1906 other difficulties have arisen between the Vienna and 
English Welsbach companies and the German Thorium Convention; 
and in 1910 the price was further lowered to a point that made the 
mining of monazite absolutely unprofitable in the Carolinas, and also 
in the interior of Brazil. The market was flooded with monazite 
until the outbreak of the European war. 

The German Incandescent Gas Light Co. of Berlin has succeeded 
during the past few years in controlling the largest manufacturers of 
thorium nitrate in Europe with the exception of those in France. 
The German concern controls now both the English and Austrian 
Welsbach companies, and consequently their thorium nitrate plant 
in Austria. This combination is the strongest competitor of the so- 
called Thorium Convention, and the latter has lost much of its power. 


The world's consumption of monazite is now about 3,000 tons per 
annum. The annual world consumption of incandescent gas mantles 
is estimated at three hundred million. The United States alone, in 
spite of the development and use of the electric metal-filament lamps, 
has consumed in the past few years some eighty million incandescent 
gas mantles as against forty million total before the year 1904. 

In the manufacture of such gas mantles about 0.5 gram of ThO 2 , 
equal to 1 gram of thorium nitrate, is used per mantle; hence, the 
world consumption of thorium nitrate is 300,000 kilos, equal to 
150,000 kilos of ThO 2 per annum. If monazite is considered to 
contain 5 per cent ThO 2 , with a 90 per cent recovery in the manufac- 
ture, 1,000 kilos (1 metric ton) of monazite will yield 90 kilos of 
thorium nitrate. The gas mantles are made of 99 per cent thorium 
and 1 per cent cerium. 

Perhaps the best work in regard to the manufacture of thorium 
nitrate and incandescent gas mantles has been written by Bohrn. 

oBohm, Richard, Das Gasgluehlicht, Die Fabrication der Gluehkoerper fuer Oasgluehlicht, Leipsic 
1905; Die Thorium Industrie: Chem. Ind., vol. 9, 1906, vol. 29, pp. 450-488. 

93290 15 -2 



Prospecting for monazite is similar to a search for gold. The 
mining pan of the batea is the most convenient apparatus in which 
to wash the gravels of the streams and separate the heavier sands, from 
among which monazite can be easily detected by its peculiar luster 
and color. Sounding rods should be employed if quick estimates 
are desirable and if the thickness and composition of the overlying 
burden in the bottom lands must be established. The concentrated 
material of the pannings is dried and sent to the chemical laboratory 
for determination of the content of thoria and other rare earths. 


It probably is not widely known that the presence of some of the 
rare earths in monazite can be easily detected by the aid of a spec- 
troscope, a pocket or hand spectroscope being sufficient. Peculiar 
as it may seem, the presence of rare earths in the monazite samples 
as taken from the pan can be at once determined by this method. 
Determination is best accomplished by spreading some of the con- 
centrated sand on a piece of paper or cloth and holding the spectro- 
scope over the. sand at a convenient angle, the natural light falling 
directly on the sand. A f airly broad dark line will appear between the 
red and the yellow of the spectrum, and another but narrower line 
will be seen in the green. These dark absorption bands seem to be 
due principally to the presence of the rare-earth oxides of neodymium, 
praseodymium, and erbium contained in the mineral. Such spec- 
trum tests for monazite can be safely relied upon when observed by 
the trained eye. The entire spectrum used is divided into a scale 
of 63 mm., the first and broader dark line becoming visible between 
the 13 and 15 mm. lines. The narrow dark line appears between 21 
and 22 mm. of the scale. 

The spectrum method of testing in the field is most helpful in fara- 
way places where a laboratory is not available. 


The monazite deposits in the Carolinas cover an area of several 
hundred square miles east of the Blue Ridge Mountains and extend 
in a southwest direction. In North Carolina the counties of Cleve- 
land, Burke, Alexander, Rutherford, and Lincoln furnish the richest 
deposits. In South Carolina the only deposits of value are in the 
counties of Cherokee and Greenville. 

Practically all of the monazite mined in the Carolinas is derived 
from the gravels in the streams and bottom lands, the miner usually 
following the old courses of the streams and creeks in the bottoms. 
The gravels are of greatly varying thickness throughout, and it is, 
therefore, difficult to arrive at a true estimate for an average value. 


From experience, however, it can be estimated that an average thick- 
ness of the monazite-bearing gravels is between 1 and 2 feet. There 
are deposits with a thickness of 3 feet and more, but they are of rare 
occurrence. The top soil in the bottom lands varies on an average 
from 3 to 6 feet, and on the outer seams of the bottom toward the 
hillsides frequently increases to a thickness of 7 feet or more. The 
top soil is barren and consists usually of sandy soil interlined with 
clays, or is of clayey matter throughout. Hydraulic methods have 
been tried on some of the richer soil deposits, but without much 


In North Carolina deposits of monazite sand are found in Burke 
County in the Brindletown district. Here monazite is obtained from 
the hydraulic washings of the gold placers. The content of monazite 
in the concentrated black sands, however, is small compared with that 
of the sluicing concentrates of other sections. The monazite in this 
section after being purified seldom shows a higher content than 3.5 to 
3.75 per cent ThO 2 . There is considerable magnetite in these sands, 
and the bulk of the concentrates consists of ilmenite (titanif erous iron) . 

McDowell County has a number of deposits in the vicinity of 
Muddy Creek. The occurrence of monazite here is closely similar 
to that of Brindletown, but perhaps contains less gold in the sand. 

In Rutherford County, within a few miles of Rutherfordton, there 
are a number of deposits that have been profitably worked for some 
time for both gold and monazite. The gold has usually been extracted 
by the miner and the residues further concentrated and shipped for 
their content of monazite. This district is especially interesting on 
account of the large area of the wide bottom lands where the gravel 
bearing monazite and gold is found to a greater extent than in most 
other sections. The percentage of monazite in the gravel, however, is 
not large, and these lands have been worked profitably only on account 
of their gold content, the monazite being obtained as a by-product. 

Much activity was shown years ago in the vicinity of Ellenboro, 
extending to Oak Spring and Sandy Run Creek and up as far as 
Duncan, which is about 18 miles from Ellenboro. The deposits in 
this region are more or less alike and the monazite obtained is of good 
grade and can still furnish considerable quantities of concentrates. 
Near Ellenboro is a hillside deposit in which monazite is found in a 
comparatively pure state in the sand of the hillside as well as in the 
gravels of the bottom lands. 

Cleveland County has a considerable area of riionazite-bea>ring 
gravels which extends between Shelby and Mooresboro via Fallston 
to a place called Zite near Carpenters Knob, a well-known peak in that 
section. The deposits around Fallston and in the entire Carpenters 
Knob region are of great importance and have furnished monazite 


concentrates of especially high thorium content. The rough concen- 
trates obtained from many of the streams in that region contain less 
black sand and garnets than those in most other sections. 

There are also fair deposits in Lincoln County about 15 miles north- 
west of Lincolnton. These deposits can also be reached from Shelby, 

Alexander County has furnished some monazite concentrates, and 
there is no doubt but that other deposits can be found in that county. 

There has been in former years considerable activity also near Hil- 
debran, Burke County, where fair deposits of considerable extent have 
been found. 


Nearly all the monazite-bearing gravel in South Carolina is found 
north of Gaffney, Cherokee County, and Cowpens, Spartanburg 
County, and in the vicinity of Greenville, Greenville County, south 
of the Southern Railway. 

There is a considerable area of monazite found in the gravels of 
the creeks and bottoms in all of these sections, and although there 
have been obtained considerable quantities of monazite concentrates 
containing 30 to 40 per cent of monazite, the bulk of the crude con- 
centrates coming from these South Carolina sections have been of 
the "black-sand" variety containing considerable ilmenite. 

Many of these deposits in both North and South Carolina have 
been described by others, and the reader is referred to the bibli- 
ography at the end of this report. 


The Idaho monazite deposits and the treatment of the gold- 
monazite-bearing sands in that State have been well described by 
Sterrett, also by Schrader, 6 and the concentration methods for the 
monazite sand used in Idaho are mentioned in the report of the 
Idaho inspector of mines for 1910. 

The monazite deposits near Centerville and Idaho City, Idaho, 
seem to be of especial importance. There is no doubt but that con- 
siderable monazite will be found in many places in the State and all the 
gravels of the deposits contain a considerable amount of gold which 
makes possible the working of such deposits for both gold and 
monazite. The gravel beds are considerably thicker than those in 
the Carolinas, and much monazite should be obtained from the 
tailings from the old gold washings. It must be remembered, how- 
ever, that the wages paid to the miners in Idaho are considerably 
higher than those paid in the Carolinas. 

Sterrett, D. B., Monazite in Idaho: U. S. Geol. Survey Mineral Resources, 1909, pp. 898-903, 1910. 
* Schrader, F. C., An occurrence of monazite in northern Idaho: IT. S. Geol. Survey Bull. 430, 1910, p. 184. 



Monazite has been found in thg State of Colorado some 20 miles 
south of Denver in the Newlands Gulch district, where the monazite 
occurs in some of the gravels, which carry also considerable gold. 
Monazite is also reported in the Platte Canyon. 


There are three kinds of deposits of monazitic sands found in 
Brazil, as follows: 

1. Deposits within the marinhas (Government lands). 

2. Deposits lying behind the marinhas that are private State 
possessions or belong to private parties. 

3. Inland deposits. 

The marinhas extend from points in the State of Rio de Janeiro 
north through the State of Espirito Santo into the State of Bahia. 

The bulk of the monazite is derived from these coast sands in the 
States of Espirito Santo and Bahia. The monazite sand at some 
places could in former years be taken off the beach by skimming the 
surface after each tide, and was pure enough to be the crude 
state. In later years, however, the material has been of consider- 
ably lower grade, so that oscillating tables have been employed, and 
some of the sands have been washed in sluice boxes wherever enough 
fresh water was obtainable. The sluice boxes used are larger and 
of a different construction than in the Carolinas, and no perforated 
plate is necessary, as there is no coarse gravel in the beach sands. 
Electromagnetic separators have also been used direct. These 
coast lands, called "marinhas," are the property of the Federal 
Government for 33 meters inland, measured from the point where 
the sea waters wash the beach at mean high tide. This method of 
marking property is uncertain, and has, of course, given rise to dis- 
putes when boundaries are established. 

At a few places along the coast are strips of monazite-bearing sands, 
lying directly behind or not far from the so-called marinhas, and some 
of these could be worked profitably were it not for the difficulties 
of proving to the Federal Government that these sands were not taken 
from the near-by marinhas. One French concern is exploiting such 
lands near Itabapoana, in the State of Rio de Janeiro, and has 
exported several hundred tons of the mineral annually for some years. 
There are several other deposits that could be worked, situated 
between Gargahu and Itabapoana; but, owing to political influences, 
no other concerns have thus far been able to obtain concessions. 

In the interior of Brazil, monazite occurs in many places, but a 
fuller description of the localities and deposits will not be given here. 

The deposits of monazite in the interior of Brazil are of a formation 
similar to those in the Carolinas, the small streams and bottom lands 


containing the only deposits of sands possessing commercial impor- 

The contents of monazite in the gravels of the streams and bottom 
lands averages about 0.25 to 0.3 per cent, a proportion about the 
same as that in the monazite in the Carolinas. There are richer 
deposits, however, in several sections. 

Along the banks of larger rivers, as, for instance, the Parahyba, 
great quantities of black sands with traces of monazite are found. 
Near Sapucaia, opposite Benjamin Constant Station on the Central 
Railway, such deposits have been worked by a French concern. They 
finally had to stop work at this point and abandon also their openings 
hi the mountainous part of this region. 

Many of the inland deposits can not be exploited on account of the 
expense of transportation of the product, the deposits being situated 
many miles from the railroad and the roads and trails being in such 
condition that it is often difficult to travel over them even with the 
mule caraven (troupa). The soft clays in the thickets of the jungle- 
like forests and the crossing of swamps make travel in many cases 
almost impossible, especially with a heavy burden laden on the mule's 
back. The rivers in most sections are not yet navigable. Frequent 
floods, caused by heavy tropical rains, and the lack of proper labor 
make difficult continuous operation in the interior of Brazil. 

At the present prices of thorium nitrate such lands in the interior 
can not be profitably exploited by any known method. When once 
the large deposits along the coast are exhausted, however, and 
the price for thorium rises, or if some other uses for the mineral and 
its rare-earth contents are discovered, then these deposits may 
become available. 


Most of the mining for monazite in the Carolinas is carried out in 
a primitive way, similar to the old methods of gold mining. The 
gravel is washed in sluice boxes without riffles, the sands being stirred 
with a square shovel, with an upward movement toward the head of 
the sluice box, the sands of higher specific gravity being thus concen- 
trated, whereas the lighter clay and some of the quartz sand are 
washed away. The gravel dug from the pit is thrown on a perforated 
plate, which is fastened over the head of the sluice box. The larger 
stones are removed from the plate. A stream of water (about 18 to 
20 gallons per minute) is fed through a spout to the gravel on the 
screen, and the sand is washed through the holes, about one-eighth 
of an inch in diameter, in the plate into the head of the box. Usu- 
ally two men are employed to each sluice box, one digging and lifting 
the gravel out of the pit to the screen and the other concentrating the 
sand by stirring it in the box with the motion described above. With 


this method much of the finer sand is lost, as the grains of sand vary 
greatly in size, and the finer, heavier grains of monazite are carried 
away by mechanical action with the lighter and coarser quartz. If 
the sands are properly sized before being washed, a much better 
result can be obtained, and practically all of the monazite contained 
in the gravel or sand can thus be saved. 

The sluice boxes are of such construction that easy transportation 
is possible, a desirable feature, because, as the gravel is worked out 
in one pit in one or two days' time, the boxes then have to be moved 
higher up the stream or bottom. It has been found more practical 
and cheaper to remove the box to the deposit than to bring the gravel 
to the box. The sluice box is usually brought over the pit, which 
has been worked out previous to the removal of the box, thereby 
furnishing, to some extent, a dumping place for the tailings that flow 
off the end of the sluice box. However, as the amount of tailings 
washed out during one day is large, the so-called "tail-raise" must 
be cleaned out with the shovel several times during the day, the tail- 
ings so removed being thrown to one side of the bank of the tail- 
raise. This is necessary in most instances, as the lands slope only 
slightly, and in some sections the bottoms and stream beds are almost 

After the sands have been concentrated in the sluice box, the con- 
centrates are often rewashed by an experienced hand and a further 
amount of useless material removed. The concentrates are then 
dried in the sun or in a form of drier usually made of a piece of 
sheet iron with turned-up edges a wood fire being built underneath. 

Many of the Carolina mines could not have been exploited had it 
not been for the fact that the people worked out the mineral on their 
own account from small deposits during times when no farm work 
could be done. They seldom figured their time of work, mined out 
what they could, and brought it to the separating plants, where they 
were paid in cash at the rate of about 8 cents per pound of pure 
monazite (machine-cleaned sand). Others were employed by some 
of the corporations at about 80 cents to $1.25 per day at the richer 
mines. It was not long, however, before new dealers arrived in the 
Carolinas, greatly inspired by the high prices which were then paid 
for the nitrate, who, knowing little of the trade, and with only crude 
means of judging the content of monazite in the washed concentrates, 
paid 12, 15, and often as high as 35 cents per pound, based on con- 
centrates containing 92 per cent monazite. This development caused 
unhealthy competition, which proved fatal to the farmers and small 
operators, as they went to large expense to produce large quantities 
of the sand, which they then held for higher prices, but could not sell 
at all when finally the market for thorium nitrate broke. To-day 
there is no mining of monazite in the Carolinas. 



The deposits are too scattered and are not extensive enough to make 
practical or profitable the use of sliming and oscillating tables. Other 
concentrating apparatus of special design can be utilized, and with 
proper sizing of the material excellent results can be obtained with 
such machines and methods, as has often been demonstrated by prac- 
tical tests. 

The concentrates produced in the sluice boxes contain 20 to 60 per 
cent of monazite. An average of about 35 per cent can be considered 
a conservative estimate as a result of practical experience. The 
concentrates have to be further refined, and are best treated by 
electromagnetic separators, of which the Wetherill-Rowand type has 
proved to be the most useful to the industry. The testing labora- 
tories of Krupp now use a new type of electromagnetic separator of 
the Ullrich type, which treats the material either "wet" or dry.. It 
is reported to have a capacity of about 2 tons of material per hour, 
which is considerably larger than that of any other type of magnetic 
separator heretofore kno'wn. The Daggett separator has also been 
used successfully for this kind of concentration. 


In the separation of monazite from other minerals and its gangue 
materials, electromagnetic methods were found to be most efficient. 

Weakly magnetic bodies can be separated from each other by em- 
ploying highly concentrated magnetic fields. Such separation is made 
possible on account of the difference in the magnetic permeability of 
different material. However, the magnetic permeability as a physical 
property can be fixed only for absolutely pure material, entirely free 
from any admixtures, as such admixtures of foreign matter influence 
considerably the magnetic relativity of the material to be treated, and 
it therefore can not be applied as a theory in the treatment of most 
minerals, which always carry a certain amount of impurities. And 
furthermore, it is impossible to bring different minerals, by known 
methods of crushing, grinding, etc., to a uniform size and shape of 
particles, as further factors, such as amount tested and whether the 
charge is packed tight or loose, affect the results, and not even com- 
paratively correct results can be obtained. Only practical tests, 
therefore, will satisfactorily determine the best results for ores and 
minerals, as on most of such electromagnetic separators the magnetic 
power can be controlled to the finest points by means of a rheostat. 
The intensity of the magnetic field must be adjusted for each specific 
separation of minerals. 

The large type of Wetherill separator has been used hi the United 
States and in Brazil for the concentration of monazite. The separator 

o See Gunther, C. G., Electromagnetic Ore Separation, 1909. See also "Bibliography on magnetic 
concentration" in Richards, R. H., Ore dressing, 1909, vol. 2, pp. 832-837. 


has two magnets of different sizes, one being nearly twice the size of 
the other. Each of these magnets has two pairs of poles, forming four 
magnetic fields and permitting a separation of two products with each 
magnet. (See fig. 1, p. 29.) The magnets are best adjusted so that 
the first pole of the first magnet removes from the sand the highly 
magnetic material, as, for instance, the magnetite and ilmenite; the 
second pole of the first magnet extracts the garnets and also the finer 
grams of ilmenite; the third magnet (being the first pole of the second 
magnet) removes all of the coarser grains of monazite; and the last 
pole extracts the finer grains of monazite. At the end turn of the 
18-inch rubber belt of the machine the residues are then dropped into 
a receptacle. This is best arranged in such manner that the residues 
are dropped from the funnel of the receptacle into the feed box of a 
small oscillating table, or other suitable means for the wet concentra- 
tion of the gold and zircon, which are often present in small quantities. 
Some fine monazite escaping with the nonmagnetic material may also 
be recovered. 


Sometimes the by-products are found to be valuable enough for 
market, and it is then of advantage to make a still finer separation, 
which can be accomplished by employing a type of separator with 
three magnets giving six magnetic fields of three different sizes 
and strengths, the last magnet being the largest and strongest. In 
this way the poles can be adjusted so that each magnetic field attracts 
and removes practically the entire amount of one certain kind of 
mineral contained in the sands, thereby giving six distinct products, 
besides all of the nonmagnetic products, which are separated at the 
end of the magnetic operation by running the residues over an oscil- 
lating table. 


The deposits of monazite sands in the Carolinas are, as has been 
previously stated, patchy, and not one single deposit is known to be 
large enough to justify the erection of a large washing and concen- 
trating plant at the mine itself. The 'magnetic separators are best 
placed at a point on a railroad, and as nearly as possible in a district 
central to many deposits. 

The percentage of monazite in the gravel averages 0.25 per cent. 
It will thus be seen that enormous quantities of crude material have 
to be handled in order to obtain a ton of marketable material about 
400 tons of gravel furnishes 1 ton of monazite. In addition, the 
quantities of barren overburden which must be removed have to 
be added. The overburden often averages more than double the 
amount of gravel to be moved. No monazite in the Carolinas can 
be mined by present methods for less than 6 to 8 cents per pound of 


monazite contained in the concentrated material as taken out of the 
sluice box. This means that to the cost of the mining must be added 
the cost of further concentration, sacking, interest on investment, 
amortization on plant, management, freight, cartage, etc. 

One man can dig and remove in nine hours (this being the usual 
working shift in the Carolinas) about 9 cubic yards of material, includ- 
ing top soil, barren sand and clay, and monazite-b earing gravel. 

The wages paid are $1 to $1.25 a day. Therefore if we take for 
a rough calculation an area of 3 square yards of ground and a depth 
of soil and gravel of 9 feet, equal to 27 cubic yards, or about 80,000 
pounds in weight, the cost would be as follows: 

For digging and removing of barren material and dump, and digging 
and removing to sluice box of the monazite-bearing gravel, 3 men 
at $1.25, 1 day each, or $3.75; for rough washing of 9 cubic yards 
of gravel in sluice box, 1 man 1 day, $1.25; final cleaning up in special 
sluice box of rough concentrates, $0.50 a total of $5.25. 

As the content of monazite in gravel is 0.25 per cent, or about 68 
pounds of pure monazite in washed concentrates, the cost is about 
7f cents per pound of monazite contained in the washed concentrates. 

The cost of transportation to the magnetic separator varies accord- 
ing to the distance over which the material has to be hauled, and 
averages about $4 per ton of monazite in concentrates, making a total 
cost of $159 per ton of monazite in concentrates. To this has to be 
added the cost of drying of the crude concentrates, and of electro- 
magnetic separation. When the plant is running to its full capacity 
(9-hour shift), turning out about 3 tons of pure monazite per shift, 
$10 for treatment, depreciation, separation, and repairs can safely 
be added to the above amount per ton of monazite. The entire cost 
of 1 ton of machine-separated monazite, containing 92 to 95 per cent 
monazite and about 4 per cent ThO 2 is, therefore, $169 at the con- 
centrating plant. To this has to be added the cost of management, 
commissions, tolls, if any, loading on cars, and freight to chemical 
plant or port. 


In concentrating monazite sands by the electromagnetic process, 
it is essential that great care be taken throughout the entire operation 
that the strength of the current is the same at all times, as the slightest 
variation will cause imperfect separation. An impure product and 
much loss of monazite will result unless this precaution is observed, 
as the monazite will be taken up by the wrong poles. This contin- 
gency is more fully illustrated below: 

If the strength of current be too great, some of the monazite will be 
mixed with the valueless ilmenite or garnets; or, if the amperage be 
too low, ilmenite or garnets will be carried over to the next following 
pole, and will then become mixed with the monazite, and, at the same 


time, too many of the liner grains of monazite will escape in the tail- 
ings. The distance between pole magnets must be carefully adjusted, 
and the number of amperes for each magnet regulated by rheostats 
for each kind of sand, for every section of the country, or even when 
from the same section different percentages of monazite and impuri- 
ties are present. 

It may be stated that a better result is obtained when the sands 
are slightly roasted before magnetic separation than if they are 
simply sun-dried or air-dried. The difference is due to the fact that 
roasting renders the material more magnetic. It has accordingly 
been found that the proper adjustment of the amperage for magnetic 
separation is quite different for sands that have been sun-dried than 
for those dried over the fire. 

Other electromagnetic separators have been used, operating on 
similar principles, but did not give as high concentrates in one oper- 
ation as the Wetherill type, although, perhaps, the new Krupp sepa- 
rator may do so. However, some other concentrators have been used 
with fair results. 

By-products usually found in the residues that can be separated by 
employing an oscillating table are zircon, rutile, gold, and sometimes 
platinum. Some of the platinum is slightly magnetic, and may be 
lost during this process of separation. 


It is difficult to give even a rough estimate of the quantities of 
monazite obtainable in the various countries where it occurs. From 
close calculations, however, it is estimated that the lands in the 
marinhas along the sea coast of Brazil may yield from 15,000 to 
20,000 tons of pure monazite. This does not include coast lands 
where the deposits have been formed in comparatively short time. 

In the interior of Brazil the writer knows of about 18,000,000 tons 
of monazite-bearing gravel deposits which should yield monazite 
containing 4^ per cent of thorium oxide; and it can be estimated that 
these gravels contain 45,000 to 60,000 tons of monazite. No doubt 
there will be found many other deposits of greater or less extent in 
the interior of Brazil, but no single deposit in the interior, so far as 
known, would warrant the erection of a large plant. In sections 
where several large deposits are found together or near each other a 
washing and concentrating plant might be profitably established, 
provided that the price for the monazite obtained were higher than 
at present (May, 1915), and especially if transportation facilities from 
the interior to the coast became better.. 

The amount of purified monazite available in the Carolinas may be 
conservatively estimated at about 15,000 to 20,000 tons (4 per 
cent ThO 2 ). 

a See table on page. 28. 


With better methods of mining and refining the moiiazite, perhaps 
those deposits could be profitably exploited at the present prices for 
monazite and thorium nitrate, especially if the mining of monazite 
were carried on in connection with the manufacture of thorium nitrate 
and inesothorium. 

It is known that attempts have been made to extract the monazite 
from the native rock, but this operation with even the richest rock 
known 0.1 to 0.2 per cent of monazite has proved to be too expen- 
sive, and such endeavors have been given up as hopeless. 



There is no duty on monozite exported from the United States. 


The duties on monazite exported from Brazil vary greatly, and 
are as follows: 


Federal Government. Duty on monazite from the marinhas 
situated along the entire coast and navigable rivers of Brazil is 
charged at the rate of 50 per cent ad valorem, and is fixed at 30, or 
about $150, per ton. Individual States have fixed duties, as follows: 

Rio de Janeiro. 651000 per metric ton (approximately $21). 

Espirito Santo. 80 per cent of selling value, established to be 
25 per ton. This duty is varying and is subject to reduction when 
applied for. 

Minas Geraes. 12 per cent ad valorem, fixed at 25 per ton and 
25 per cent ad valorem, fixed at 25 per ton, plus 2 specific duty. 


The duty on monazite imported into the United States has been 
6 cents per pound, but was reduced to 4 cents in 1910, and is now 
25 per cent ad valorem. 

The import duty on mantle ashes is $10 ad valorem. 

The import duty on nitrates has been 25 per cent ad valorem. 


The following features should be ascertained in the investigation 
of monazite deposits for exploitation: 

1. Extent and depth of the monazite-bearing alluvial deposits, 
sands, and gravels in river beds and bottoms. 

2. Amount and character of barren overburden overlying the gravel 
or sand deposit. 

3. The percentage of monazite contained in the raw material to 
be treated. 


4. Percentage of thorium oxide contained in the monazite. 

5. Transportation facilities and cost of transportation. 

6. Water conditions rain-fall throughout the year and water 
supply for concentrating purposes and for the boiler. 

7. Timber obtainable on or near property for building use, fuel, 

8. Depth and character of bedrock. 

9. Occurrence and character of clays. 

10. Power available. 

11. Labor, also conditions for housing. 

12. Mining laws. 

13. Cost of supplies. 

14. Import and export duties. 

15. Best-suited methods for exploitation (concentration, etc.) 

16. Quantities and value of by-products and methods of obtaining 

17. Dumping ground. 

18. Inclination of surface of property. 

These points having been thoroughly determined, and also 
whether the existent volume of material, together with other condi- 
tions, will warrant exploitation and the erection of a plant, it should 
be concluded from the topographic features which methods of exploi- 
tation of the material will be most suitable. 

In determining the average extent and depth of such alluvial 
deposits great care must be taken to ascertain the situation of the 
old channels of the streams, as many of the deposits in bottom lands 
are irregular, so that a true estimate of the amount of gravel or sand 
contained can be given only after thorough testing by way of sound- 
ings, and especially by opening test pits at short distances from 
each other. As the percentage of the mineral contained in the 
gravels is small and the thickness of the deposit is usually slight, it 
will be realized that an enormous area of gravel and sand deposit 
must be within easy reach to insure profitable exploitation. The 
relation of volume to richness is therefore a most important con- 

Transportation is a feature that has to be well considered. 

In sections in the Carolinas quickly rising streams and sudden 
torrents have destroyed dams and carried away sluice boxes, imple- 
ments, and other materials obtained by hard labor. Uncovered 
deposits have been covered up again with the sands and mud brought 
from the mountains duiing such torrents. Rich deposits have also 
been purchased during favorable seasons, which could ordinarily 
be worked during short periods only, on account of lack of water or, 
in winter, hard frozen gravel, the thawing of which was too expensive. 
Had the conditions been properly studied, much loss might have been 


Careful forethought regarding a dumping ground should be made 
in all developments, for large quantities of bowlders, clay, and tail- 
ings are produced. The deposits may become choked because the 
refuse material is dumped in an undesirable place, causing further work 
to be abandoned, as the removal of dump material is costly. 

Clays give great trouble when present as an overburden or, as is 
of frequent occurrence in the Carolinas, when mixed in large quanti- 
ties with the gravel. The removal of the clayey overburden is much 
more expensive than removal of sandy materials, and when the clay 
is mixed with gravel washing consumes more tune and large volumes 
of water. 

When clay is mixed with gravel, particular care must be used 
in removing it, as much monazite may adhere to it. The clays 
seldom contain any of the mineral, but the mineral becomes embedded 
in the outer parts of the clay while lying in the alluvium. The 
practice of cutting up the clay is useless and wasteful, although this 
method has been followed by some of the operators. It is sufficient 
to wash the surface of such clays carefully and then remove them 
to the dump. 


Attempts have been made to utilize by-products from Carolina 
monazite. Twenty tons or more of ilmenite has been shipped to 
Europe, but could not bear transportation costs. Garnets derived 
from the separators have been widely offered, but have been found 
to be of no value as abrasives, the grains being rounded off by the 
constant friction while rolling along with other sands in the stream 
beds. The larger particles of garnets obtained by classification, 
which could have been crushed, and thereby had their sharp edges 
preserved, have been obtained in small quantities only from the 
monazite sands. 

In some sections gold is found in the concentrates. Although 
the amount so obtained has been small, it has paid to put aside the 
residues after treatment by electromagnetic methods, and then, 
when sufficient quantities have been collected, to concentrate them 
on an oscillating table or by some other suitable process. Although 
the proportion of gold contained in such sands is not great, it has 
been known to have a value of about $200 per 30 tons of monazite, 
which is equal to about 1| cents per ton of gravel. This could be 
considered almost clear profit, as the extraction of the gold from the 
residues is inexpensive. Monazite sands purchased from gold- 
mining sections, which have been treated for gold by the miners, 
have, after the separation of the monazite, yielded a further small 
amount of the precious metal. 

In many sections "black sands" accompany monazite in large 


In this paper methods of treatment in actual use have been de- 
scribed. It is, however, more than probable that small dredges 
would prove useful in the mining of monazite as they have in the 
western field for gold. 


Many methods for determining thorium in monazite have been 
described. Only the following well-known method is alone given 

About 1 gram of the monazite is ground to an impalpable powder, 
weighed into a platinum vessel, covered with 15 to 20 c.c. of con- 
centrated sulphuric acid, and evaporated until fumes are no longer 
driven off. More sulphuric acid is added and heated as before. 
The operation is repeated several times until the conversion of the 
phosphates into sulphates is complete. The mass resulting is added 
in small quantities to about 700 c.c. of water at C., with constant 
stining, care being used not to allow the temperature to rise higher 
than 2 C. The solution is allowed to stand 10 to 12 hours, when 
it is filtered and washed. The filtrate is then nearly neutralized 
with dilute ammonia, 50 c.c. of a cold saturated solution of oxalic 
acid is added with constant stirring, and the solution is allowed 
to stand for 12 hours. The solution is then filtered and the precipi- 
tate washed well with water. The precipitated oxalates are then 
washed into a beaker, and treated with a strong solution of caustic 
potash, heated to boiling, diluted, and filtered. 

The hydroxides are washed thoroughly with water and dissolved 
off the filter with hot dilute hydrochloric acid (1-1). The solution 
is evaporated to dryness to free it from acid, taken up with 75 to 
100 c.c. of water, 15 c.c. of a saturated solution of sodium thiosul- 
phate is added, and the solution is heated to boiling. It is then 
filtered and the precipitate and the filter set aside for subsequent 
filtration. An excess of ammonia is added to the filtrate, the pre- 
cipitate is filtered off, washed, dissolved in hydrochloric acid, and 
evaporated to dryness, the residue being taken up in water and 
reprecipitated with thiosulphate as before. The solution is filtered 
through the filter paper carrying the first precipitate, and the filtrate 
is treated as before. The precipitations are continued as long as the 
precipitate forms with the thiosulphate, three precipitations usually 
being sufficient to completely extract the thorium. The combined 
precipitates of thorium-thiosulphate are washed completely, dried, 
and ignited. The ignited mass is fused for some time with potassium 
bisulphate, taken up in water, and a few drops of hydrochloric acid 
added, and precipitated with oxalic acid. The oxalates are converted 

a. SeeMetzger, F. J., Anew separation of thorium from cerium, lanthanum, and didymium, and its appli- 
cation to the analysis of monazite, Jour. Am. Them. Soc., vol. 24, 1902, p. 901: see also Levy, S. 1 ., The 
rare earths, London, 1915, pp. 2 .5-290. 


into the hydroxides, dissolved in hydrochloric acid, evaporated to 
dryness, taken up in water, and reprecipitated with sodium thiosul- 
phate, filtered, washed, dried, ignited, and weighed as ThO 2 . 


Soddy gives in a short form the technical treatment of the 
monazite sand as it is carried on to-day in the industry. 

In the first stage of the technical treatment of the monazite sand, 
which is ground up very fine, it is heated with twice its weight of 
sulphuric acid. The further procedure in the treatment is described 
by Soddy 6 as follows : 

The cold mass is dissolved in water and left to settle. The solution is then frac- 
tionally precipitated with magnesia, the thorium being concentrated mainly in the 
first fractions precipitated. The commonest and most useful reagent for precipitating 
the rare earths from a solution containing common earths such as alumina, iron, etc., 
is oxalic acid. Now thorium oxalate is of all the rare-earth oxalates the least soluble 
in acids, so that by working in fairly strong nitric acid solution thorium oxalate may 
often be precipitated and separated at least partially from the other rare earths and 
from calcium. The same is true of the rare-earth phosphates, that of thorium being 
one of the most insoluble in dilute acids. On the same principle thorium is often 
precipitated by weak bases, such as the substituted ammonias, for example, dimethyla- 
mine, while zirconium, etc., remain dissolved. The potassium salt of hydrazoic 
acid, KN 3 , precipitates thorium hydroxide only from mixtures of thorium and cerium 
on boiling. The same separation may be effected by means of sodium thiosulphate 
on boiling, thorium alone being separated, as hydroxide. This ready hydrolysis of 
weak thorium is characteristic of the element. The oxalatos of thorium and zirconium 
alone of the rare earths are soluble in ammonium oxalate, and on strongly acidifying 
the solution the former alone is reprecipitated. The solution of the oxalate of tho- 
rium and its conversion into soluble salts may be effected by means of concentrated 
ammonium or sodium carbonate and precipitation of the concentrated solution as 
thorium hydroxide with strong ammonium or sodium hydrate. Thorium is distin- 
guished from the yttrium group of the rare earths by ite power of forming a double 
sulphate with potassium sulphate, insoluble in excess of the latter reagent, and so 
may be separated from a mixture of the sulphates by saturating the solution with 
potassium sulphate. Alike in the old, now obsolete, as in the present, technical 
methods of purifying thorium, the peculiar solubility relations of thorium sulphate 
in water have been largely applied. The older method consisted in volatilizing the 
excess of sulphuric acid from the material being treated, and in dissolving the 
anhydrous sulphates in ice-cold water a tedious operation and in heating the 
solution till the hydrated thorium sulphate was precipitated. The latter was then 
dehydrated, at 300 to 400 and the process repeated. In present practice the sul- 
phuric acid is always kept in great excess in the initial treatment of the mineral, 
but the sulphate method may be employed at the final stage of manufacture as follows: 

The thorium hydroxide is dissolved in hydrochloric acid, so that the solution 
contains not more than 30 per cent ThO 2 , and sulphuric acid is added to the extent 
of 0.5 per cent more than the equivalent quantity, the temperature being kept low, 
and in any case below 40 as a maximum. , Under these conditions the hydrate 
Th(SO 4 )28H 2 O is precipitated, departure from the conditions causing the separation 

a Soddy, Frederick, The chemistry of the radio elements, 1911, pp. 64-69; see also, Bohm., Richard, Die 
Darstellung der seltenen Erden, Leipzig, 1905, vol. 2, pp. 94-98; Levy, S. I., The rare earths, Lon- 
don, 1915, pp. 276-285. 

b Soddy, Frederick, loc cit. 


of the tetrahydrate, which is in every way less easily manipulated. The precipitated 
sulphate is reconverted into hydroxide, and the process repeated as often as necessary 
to remove all impurities. 

Thorium forms a curious compound with acetyl acetone, Th(C 5 H 7 O 2 ) 4 , which is 
soluble in chloroform and alcohol, and can be distilled in a vacuum, and so can 
advantageously be employed for the purification and separation of the element. 

It may be mentioned that in the fusion of refractory minerals, as with sodium 
carbonate, the thorium, if present, is converted into the highly insoluble oxide, 
Th0 2 , and its presence is apt to be overlooked . 

Thanks largely to the thorium industry, in which a product unusually pure Is 
essential, there exist, therefore, a great variety of exceedingly good and sharp methods 
for the separation and purification of thorium, and it muet be understood that ionium, 
if present, and radio-thorium always remain unseparated from thorium in these 
processes as far as they have been examined. 

In the manufacture of- thorium nitrate from monazite a large amount 
of residues of the cerium group of rare earths is ob tamed. Monazite con- 
tains 60 to 70 per cent of the cerium group or other rare earths besides 
thorium, and 3,000 tons, which is the annual consumption of mona- 
zite, gives about 1,000 tons of cerium and about 1,200 tons of a mix- 
ture of the rare earths, lanthanum, neodymium, and praesodymium 
oxides. Considerable research work has been done in order to utilize 
these waste materials, and experiments have been made with almost 
every one of them. In order to obtain and separate the rare-earth 
elements, thousands of crystallizations and fractionations are neces- 
sary, although cerium itself is separated with comparative ease. The 
untiring work carried on in the research laboratories of the industries 
as well as by the scientists in both America and in Europe will, no 
doubt, in time be crowned with successful technical applications of 
the by-products. 


Monazite sand is the main source of mesothorium and contains also 
uranium and, consequently, radium. Mesothorium has properties 
similar to radium, and the radium therefore is separated together with 
the mesothorium. The methods employed in the extraction of meso- 
thorium are well known and have been described by Haitinger and 
Ulrich , and have been used in the extraction of radium. 6 

Some manufacturers of mesothorium add a small quantity of barium 
sulphate to the monazite sand during its treatment with sulphuric 
acid, whereby the mesothorium is separated with the insoluble material 
left after the treatment of the product with water. 

The half-value period or period of half life (the time required in 
which one-half of any given quantity of radioactive matter disinte- 
grates becomes transformed is called half-value period or period of 

o Haitinger, Ludwig, and Ulrich, Karl, Bericht iiber die BearbeitiniK der Pechblendo 
Her. K. Akad. Wiss., vol. 117, 1908, p. 619. 

6 Moore, R. B., and Kithil, K. L., A preliminary report on uranium, radium, and vanadium: Bull. 70, 
Bureau of Mines, 1914, p. 79. 


half life) of meso thorium is 5.5 years, whereas that of radium is ahout 
2,000 years. 

The manufacture of mesothorium alone from monazite is not prof- 
itable, as the value of the mesothorium extracted would not pay for 
the cost of the monazite. As a by-product from thorium nitrate man- 
ufacture such manufacture should be of importance. 


The quantitative determination of mesothorium is carried on in 
the same manner as for radium. 

The content of mesothorium in preparations, all of which carry 
about 25 per cent of radium, is expressed in terms of the gamma ray 
activity of radium in equilibrium. For example, 5 milligrams of 
mesothorium on this standard indicates that the gamma ray activity 
of the mesothorium plus the radium contained in it one month after 
separation gives a gamma ray activity equal to that of 5 milligrams 
of pure radium bromide. 

If both the radium and the mesothorium are to be determined then 
radium plus mesothorium is determined by means of the gamma ray 
method, and afterwards, by the emanation method, the radium alone 
is determined. 

By the gamma ray method alone can be determined the ratio of 
radium to mesothorium by measuring the gamma rays before and 
after boiling the solutions. The content of mesothorium plus radium 
is found before the solution is boiled ; after it has been boiled, the con- 
tent of mesothorium alone is given, as the radium emanation is re- 
moved by boiling, and radium C t , which emits the gamma rays, is, for 
all practical purposes, disintegrated after three hours' time. 

In regard to the method of measuring mesothorium and radium by 
the gamma ray method, reference is made to the work of Ebler, b and of 
Meyer and Hess. c 

The quantities of mesothorium that can be extracted from monazite 
are, of course, very small. One hundred metric tons of monazite with 
a content of 5 per cent ThO 2 contains approximately 4.3 tons of tho- 
rium metal. According to Rutherford, d one metric ton of thorium 
metal contains 0.42 milligram of mesothorium. We have, therefore, 
0.42 milligram of mesothorium per weight of 10~ 6 grams of tho- 
rium, or 4.3 times 0.42, equals 1.8 milligrams of mesothorium by 
weight. The activity due to mesothorium is three times as great as 

o Soddy, Frederick, The chemistry of the radio elements, 1911, pp. 46-49; Rutherford, E., Radioactive 
substances and their radiations, 1913, p. 550. 

6 Ebler, Erich, Chemiker Kalender for 1914, vol. 2, pp. 371-372. 

c Meyer, Stefan, and Hess, V. F., Gamma Strahlenmessung von Meso-thorpriiparaten: Mitt. Inst. Ra- 
diumforschung, Vienna, July 2, 1914, pp. 1443-1458. 

d Rutherford, E., Radioactive substances and their radiations, 1913, p. 552. 



that due to radium when compared weight with weight. The meso- 
thorium obtained from one ton of monazite, therefore, would be cal- 
culated as 5.4 milligrams. Lorenzen, however, states that tech- 
nically 2.5 milligrams of mesothorium can be obtained from 1 metric 
ton of monazite, or 100 tons of monazite would yield 250 milligrams 
of mesothorium. It seems, therefore, that technically a recovery of 
about 50 per cent is made. Mesothorium is sold on the basis of its 
activity compared with radium bromide of highest purity (determined 
by the gamma ray method), and has been sold with increasing de- 
mand at $45 to $60 per milligram. The separation of mesothorium 
has been widely discussed in scientific and technical papers and is 
outlined on page 25. 

The manufacture of thorium nitrate from monazite is well known 
and has been described extensively. This manufacture, however, is 
briefly described on pages 24-25. The manufacture of the thorium 
nitrate is so highly developed that a recovery of 90 to 95 per cent of 
the thorium contained in the monazite has been made by many indus- 
trial concerns. 

Although in former years monazite and thorium nitrate were 
imported into this country, lately, since the manufacture of meso- 
thorium from the thorium residues has been begun, Europe prefers 
to export the ash of the broken incandescent mantles, which are high 
in ThO 2 , and keeps the monazite in order to obtain the mesothorium 
from the residues. The import duty on the ash brought into the 
United States is only 10 per cent ad valorem, whereas thorium nitrate 
pays 25 per cent duty. The thoria ash has been sold for 25 marks 
($6) per kilogram in Europe. 


The minerals contained in monazite sands, arranged according to 
their specific gravity, are shown in the tabulation following: 

Minerals contained in monazite sands, arranged according to specific gravity. 







tive oc- 



tive oc- 



2 05 


42 to 4 25 



2.5 to 2.7 


4.5 to 4. 7 



3.0 to 3. 2 


4.5 to5 




3.2 to 3. 25 
3.2 to 3. 5 



4.8 to5.3 
5. 16 to 5. 18 



33 to 3. 6 


15 to 19 



3.8 to 4. 3 


a- Private information received from Juliu.s Lorenzen, Tegel-Berlin, on Chemical Manufacture of Meso- 
6 The order varies according to localities. 



The conglomerate must be freed from the larger gravels and from 
the clays. 

Proper sizing is important before concentration; in sizing the 
remaining clay and mica particles should be removed by a sliming 

Four or five sizes should be made through sieves of 20, 50, 80, and 
100 mesh. 

Such properly sized material when treated on the large type of 
Wetherill electromagnetic separator, having two magnets and 18-inch 
belt, gives the following results : 
Results of action of Wetherill electromagnetic separator on properly sized monazite sands. 



Point in separator at which mineral separated. 


Magnetite ' 

Ilmenite 1 

Hematite i 

Platinum (if any) 


Second pole, first magnet; distance between poles, about 


Olivine ." 

Monazite (92 to 95 per cent) 
and traces of zircon and 
Platinum, etc. (if any) 

First and second pole of second magnet; distance, first pole, 
6 mm.; second pole, 2 to 3 mm. 

12 to 15 am- 


Residues off belt were quartz, feldspar, gold, zircon, rutile, etc. 

Data showing fluctuation of prices for thorium nitrate for use in incandescent gas 

(per kilo). 

States (per 

1894 . . 



1895 July 

1895, November . . . 

1896, early part 
1896 later part 







1904, later part 


1907, early part.... 

1907 later part 

1908* . . 


1910 later part 


1913, later part 

1914, early part 
1914, later part 

Price of thorium 

"Import duty on thorium nitrate brought into the United States, 25 per cent ad valorem. 
6I)ata furnished by Dr. Hugo Liebcr, 25 Madison Avenue, New York, N. Y. 


A flow sheet of the separation process is shown in figure 1. 



Zircon and rutile 

Quartz and f eld- 

Slime and lighter 

FIGURE 1. Flow sheet, showing steps in process of magnetic separation of monazite sands. 


BOHM, RICHARD. Die Darstellung der seltenen Erden, 2 vole., Leipzig, 1905. 

- Die Venvendung der seltenen Erden, Leipzig, 1913. 

- Monazite sand: Eng. and Min. Jour., vol. 81, May 5, 1906, p. 842. 

- Die Thorium Industrie: Chem. Ind., vol. 29, 1906, pp. 450-488. 

DAY, D. T., and RICHARDS, R. H. Useful minerals in the black sands of the Pacific 
Slope: TJ. S. Geol. Survey, Mineral Resources for 1905, 1906, pp. 1175-1258. 

GUNTHER, G. G. Electromagnetic ore separation, 1909, 193 pp. 

JOURNAL OF THE FRANKLIN INSTITUTE. Report on Welsbach light, by Committee on 
Science and Arts. Vol. 150, December, 1900, pp. 406-415. 

JOHNSTONE, S. J. Monazite from some new localities: Jour. Soc. Chem. Ind., vol. 
33, January 31, 1914, pp. 55-59. 

LANEY, F. B., and WOOD, K. H. Bibliography of North Carolina geology, miner- 
alogy, and geography: N. C. Geol. and Econ. Survey Bull. IS, 1909. Gives a 
comprehensive bibliography concerning monazite deposits in North Carolina. 

LEVY, S. I. The rare earths, their occurrence, chemistry, and technology. London, 
1915, 345 pp. 

LINDGREN, WAI.DEMAR. Mining district of Idaho Basin and Boise Ridge: U. ,S. Geol. 
Survey, Eighteenth Annual Report, pt. 3, 1898, pp. 617-744; The monazite sands, 
pp. 677-679. 

METZGER, F. J., and ZONS, F. W. A volumetric method for the determination of 
thorium in the presence of other rare earths. The analysis of monazite sand: 
Chem. News, vol. 107, March 7, 1913, pp. 112-113. 

MINING REPORTER. The industrial position of thorium. Vol. 53, February 22, 1906, 
p. 190. 

NITZE, H. B. C. Monazite, U. S. Geol. Survey, Sixteenth Annual Report, pt. 4, 1896, 
pp. 667-693. 

- Monazite and monazite deposits in North Carolina: N. C. Geol. Survey Bull. 
9, 1895, p. 47. 

PRATT, J. H. Monazite: U. S. Geol. Survey, Mineral Resources, 1901-1905. 
PRATT, J. H., and STERRETT, D. B. Monazite and monazite mining in the Carolinaa: 

Trans. Am. Inst. Min. Eng., vol. 40, 1910, pp. 315-340. 
RICHARDS, R. H. Ore dressing. 1909, vol. 2, pp.832-837. Contains bibliography 

of magnetic ore concentration. 
SCHRADER, F. C. An occurrence of monazite in northern Idaho: U. S. Geol. Survey 

Bull. 430, 1910, pp. 184-191. 
SLOAN, EARLE. Catalogue of mineral localities in South Carolina: S. C. Geol. Survey 

Bull. 2, 1908, pp. 129-142. 
STERRETT, D. B. Monazite: U. S. Geol. Survey, Mineral Resources, 1906-1910. 

- Monazite deposits of the Carolinas: U. S. Geol. Survey Bull. 340, 1908, pp. 

TRUCHOT, P. Occurrences and extraction of thorite, monazite, and zircon: Chem. 
News, vol. 77, pp. 134-135, 145-147, 1898. 


A limited supply of the following publications of the Bureau of 
Mines is temporarily available for free distribution. Requests for 
all publications can not be granted, and to insure equitable distribu- 
tion applicants are requested to limit their selection to publications 
that may be of especial interest to them. Requests for publications 
should be addressed to the Director, Bureau of Mines. 

'BULLETIN 3. The coke industry of the United States as related to the foundry, by 

Richard ^ 1enke - 191 - 32 PP- 

BULLETIN, " n Apparatus and methods for the sampling and analysis of furnace gases, 
by J C. W. j : azer an d E. J. Hoffman. 1911. 22 pp., 6 figs. 

BULLETI! *> The uses of peat for fuel and other purposes, by C. A. Davis. 1911. 

214pp.. I*' 1 -' !"* 

-g T ^LETiN 42. The sampling and examination of mine gases and natural gas, by G. 
Burrell and F. M. Seibert. 1913. 116 pp., 2 pis., 23 figs. 

BULLETIN 45. Sand available for filling mine workings in the northern anthracite 
coal basin of Pennsylvania, by N. H. Darton. 1913. 33 pp., 8 pis., 5 figs. 

BULLETIN 47. Notes on mineral wastes, by C. L. Parsons. 1912. 44 pp. 

BULLETIN 53. Mining and treatment of feldspar and koalin in the southern Appa- 
lachian region, by A. S. Watts. 1913. 170 pp., 16 pis., 12 figs. 

BULLETIN 64. The titaniferous iron ores of the United States, their composition and 
economic value, by J. T. Singewald, jr.. 1913. 145 pp., 16 pis., 3 figs. 

BULLETIN 70. A preliminary report on uranium, radium, and vanadium, by R. B. 
Moore and K. L. Kithil. 1913. 101 pp., 4 pis., 2 figs. 

BULLETIN 71. Fuller's earth, by C. L. Parsons. 1913. 38 pp. 

BULLETIN 81. The smelting of copper ores in the electric furnace, by D. A. Lyon 
and R. M. Keeney. 1914. 80 pp., 6 figs. 

BULLETIN 84. Metallurgical smoke, by C. H. Fulton. 1914. 94 pp., 6 pis., 15 figs. 

BULLETIN 85. Analyses of mine and car samples of coal collected in the fiscal years 
1911 to 1913, by A. C. Fieldner, H. I. Smith, A. H. Fay, and Samuel Sanford. 1914. 
444pp., 2 figs. 

TECHNICAL PAPER 3. Specifications for the purchase of fuel oil for the Government. 
with directions for sampling oil and natural gas, by I. C. Allen. 1911. 13 pp. 

TECHNICAL PAPER 8. Methods of analyzing coal and coke, by F. M. Stanton and 
A. C. Fieldner. 1913. 42 pp., 12 figs. 

TECHNICAL PAPER 14. Apparatus for gas-analysis laboratories at coal mines, by 
G. A. Burrell and F.M. Seibert. 1913. 24 pp., 7 figs. 

TECHNICAL PAPER 38. Wastes in the production and utilization of natural gas, and 
means for their prevention, by Ralph Arnold and F. G. Clapp. 1913. 29 pp. 

TECHNICAL PAPER 39. The inflammable gases in mine air," by G. A. Burrell and 
F. M. Seibert. 24 pp., 2 figs. 

TECHNICAL PAPER 41. Mining and treatment of lead and zinc ores in the Joplin 
district, Missouri; a preliminary report, by C. A. Wright. 1913. 43 pp., 5 figs. 

TECHNICAL PAPER 43. The influence of inert gases on inflammable gaseous mixtures, 
by J. K. Clement. 1913. 24 pp., 1 pi., 8 figs. 

TECHNICAL PAPER 50. Metallurgical coke, by A, W. Belden. 1913. 48 pp., 1 pi., 
23 figs. 



TECHNICAL PAPER 60. The approximate melting points of some commercial copper 
alloys, by H. W. Gillett and A. B. Norton. 1913. 10 pp., 1 fig. 

TECHNICAL PAPER 66. Mud-laden fluid applied to well drilling, by J. A. Pollard and 
A. G. Heggem. 1914. 21 pp., 12 figs. 

TECHNICAL PAPER 70. Methods of oil recovery in California, by Ralph Arnold and 
V. R. Garfias. 1914. 57 pp., 7 figs. 

TECHNICAL PAPER 76. Notes on the sampling and analysis of coal, by A. C. Fieldner. 

1914. 59 pp., 6 figs. 

TECHNICAL PAPER 81. The vapor pressure of arsenic trioxide, by L. H. Duschak. 

1915. 22 pp., 2 figs. 

TECHNICAL PAPER 88. The radium-uranium ratio in carnotites. by S. 0. Lind :uid 
.C. F. Whittemore. 1915. 29 pp., 1 pi., 4 figs. 

TECHNICAL PAPER 89. Coal-tar products, and the possibility of their successful 
manufacture in the United States, by H. C. Porter, with a chapter on coal-tar prod- 
ucts used in explosives, by C. G. Storm. 1915. 21 pp. 

TECHNICAL PAPER 90. Metallurgical treatment of the low-grade am) ( . n ,,.j,i ex on , s 
of Utah; a preliminary report, by D. A. Lyon, R. H. Bradford, S. S- J^entz Q < 
Ralston, and C. L. Larson. 1915. 40 pp. 

TECHNICAL PAPER 95. Mining and milling of lead and zinc ores in tru 
district, Wisconsin, by C. A. Wright. 1915. 39 pp., 2 pis., 5 figs. 

TECHNICAL PAPER 99. Probable effect of the war in Europe on the ceramic' iml., 
tries of the United States, by A. S. Watte. 1915. 15 pp. 


Date Due 

DEC 2 












Syracuse, N. Y. 
Stockton, CaMf. 

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